1. Technical Field
The present invention relates to a display device such as an electrophoretic display device, for example.
2. Related Art
As a display device of this type, electrophoretic display devices used for electronic books or the like are disclosed in JP-A-2005-25163 and International Publication No. 2001/091096, for example. In JP-A-2005-25163, an image input by hand (by a pen) is overwritten onto a normal image (an image input by other than a pen) so that a display image is rewritten. To be more specific, when a normal image is displayed, after entire white display is performed by reset-driving, an image is written by writing-driving. On the other hand, when an image is input by hand, only writing-driving is performed without reset-driving. In the latter case, partial writing is performed on pixels included in a pen input region such that the pixels display a darkest state (black) (for example, second embodiment).
If such partial rewriting is repeatedly performed, afterimages are accumulated. This causes a risk that a display image is disturbed. International Publication No. 2001/091096 discloses a technique of executing a refresh operation every time a predetermined period of time passes in order to prevent deterioration in image quality due to image disturbance. It is to be noted that in a display device, the refresh operation may be performed every time rewriting is performed a predetermined number of times in addition to or instead of every predetermined time depending on cases.
However, in International Publication No. 2001/091096, a trouble that an image disturbed due to partial rewriting is visually recognized by a user who uses an electronic book or the like for a relatively long period of time until a predetermined period of time passes is caused. Further, a following trouble is also caused. That is, even in a case where partial slight disturbance is caused on a display image in a screen due to partial rewriting, a refresh operation (or reset-driving) is automatically performed on the entire screen. Therefore, a cancellation screen with the entire black or white display is visually recognized by a user frequently and thus user's convenience is impaired.
In order to solve the problems, it can be considered that pixels located only in a region on which partial rewriting has been performed every partial rewriting in a screen are subjected to reset-driving. In this case, a difference in contrast is caused between a region on which reset-driving has been performed and other regions due to a difference in an elapsed time since writing has been performed or the like. In addition, there arises a problem that partial rewriting is delayed because of the reset-driving.